Wallis Simpson has been demonized for decades as the Baltimore divorcee who scandalized Britain by luring Edward VIII, the Prince of Wales, from his short tenure on the throne.

His abdication -- touched on in the 2010 film, "The Kings Speech," and most recently in a sympathetic biopic from Madonna, "W.E." -- caused an unprecedented constitutional crisis in 1936 and she was thereafter seen as "that woman."

And now, a new biography, "That Woman: The Life of Wallis Simpson," suggests that the "mannish" social climber with the "beautiful dark sapphire blue eyes, full of sparkle and nice mischief" may have been intersex.

Author Anne Sebba points to the Duchess of Windsor's raspy voice, square jaw and flat chest as signs, among other physical manifestations, that she was born male.

She describes a flirtatious debutante with a voracious sexual appetite, trained in the Chinese art of seduction and comfortable with oral sex, an unlady-like talent in the early 20th century.

An estimated 1 in 2,000 children born each year are neither boy nor girl -- they are part of a group of about 60 conditions that fall under the diagnosis of disorders of sexual development.

Once called hermaphrodites, from the handsome Greek god who had dual sexuality, they have been described in literature for centuries, from Judaism's the Talmud, to the Pulitzer-winning novel, "Middlesex."

"People from time immemorial have had accidents of nature and presented kids with partially formed genitals that they didn't understand," said Dr. Norman Spack, an endocrinologist and co-director of the Gender Management Service at Children's Hospital in Boston.

Simpson was born in 1896, has been dead for 26 years, and it is highly unlikely anyone will ever know if she was truly intersex, he said.

As for speculation that her "mannish demeanor" is evidence of being intersex, Spack said he has "scientific and philosophical problems" with that premise.

The biography suggests that Wallis may have been born with complete androgen insensitivity syndrome (CAIS).

Those born with CAIS are fully female, except for the absence of a uterus or ovaries, so they can neither menstruate nor reproduce.

Girls with CAIS have the male XY chromosomes, but because the hormonal virilization process does not occur in the early stages of gestation, they never develop external male genitals -- they remain female -- or internal female organs such as ovaries or uterus. As a result, they are infertile.

"There are several prominent actresses today in America -- I can't reveal their names -- who have CAIS," said Spack. "They are mothers with adopted children and they are women, of course."

These women can have sexual intercourse and they also report normal sensation, because nerve endings are still present.

Children with CAIS have a mutation in the androgen receptor gene that makes it impossible for the body to deliver testosterone to the developing fetus.

The genetic defect is carried in the mother's X chromosome and passed on to 50 percent of their male children, who "come out looking female," according to Spack.

In the first six to seven weeks of gestation, the genital area is undifferentiated. "There is no difference between the sexes," he said. "The structures can go either way."

Male hormones stimulate the tissue to form a phallus, seminal vesicles and sperm ducts, rather than a clitoris, uterus and Fallopian tubes.

Normally, development of testes and are driven by specific genes in the Y chromosome. One hormone gets rid of the female internal structures and cells in the testes generate testosterone to form the internal and external male genitals.

In CAIS, normal testes are formed, but there is no penis, nor are there internal female organs. The undifferentiated "cleft" appears as a vagina.

"The newborn looks like a perfectly normal girl," said Spack.

CAIS can be diagnosed at several stages, most often in women over 35 during an amniocentesis, chromosome analysis and an ultrasound. Sometimes, it's never discovered until puberty, when there is no menstruation, or during hernia surgery.

"Twice a year, I get a call from the operating room that there is a perfectly normal little girl with a hernia in the groin," said Spack. "The surgeon looks in the hernia sac and it's an obvious testis, which can be confirmed by frozen section biopsy."

Upon further examination, the vagina is shortened with no cervix at the back. "Some girls don't get looked at until they are 15 or 16 even if they are sexually involved."

"The vagina is expansive and can accommodate so their sexual potential is not a big issue," said Spack.

"Our chromosomes don't tell us who we are," Dr. Arlene Baratz, a Pittsburgh breast radiologist who has two CAIS daughters, told ABCNews.com last year. "We expect XX is pink and a girl and XY is blue and a boy, but we know from children with gender identity conditions that is not always the case, even when their bodies are perfectly typical."

When Baratz's daughter Katie was 6, doctors discovered small testes in a hernia sac. Today, in her late 20s, she hopes one day to adopt a child.

"These girls look completely female and they are girls," said her mother. When these babies are gender assigned as female, 99 percent of them go on to feel like women when they grow up.

Unlike Wallis, girls with CAIS tend to be tall -- she was 5-feet, 7-inches tall. "They also tend to be buxom," said Spack.
"Wallis was flat as a board."

They also have "scant genital hair" and rarely need to shave their underarms and legs. Their mothers, as carriers of the genetic mutation, tend to have less sexual hair than sisters who are not carriers, according to Spack.

As for raspy voices and male musculature, as was described in the Wallis biography, that is not the case, he said. The testes, if present, compensate for lack of testosterone and -- in a biological contradiction -- produce "sky high" testosterone that converts to estradiol, which feminizes these women.

After puberty, doctors usually, but not always, remove the testes because they can become cancerous, and intersex women take estrogen supplements to maintain feminization.

As for the Wallis biography, the author suggests her personality traits confirmed she was intersex -- a premise that Spack finds blatantly sexist by today's mores.

Sebba says that a German graphologist who analyzed her handwriting determined Wallis was, "a woman with a strong male inclination in the sense of activity, vitality and initiative. She must dominate, she must have authority, and without sufficient scope for her powers can become disagreeable. She is ruled by contradictory impulses."

But being "brash" and "having balls" and liking oral sex don't define intersexuality, according to Spack.

Reports about Wallis in British tabloids like the Daily Mail made Spack "recoil a bit," he said.

"She is just a woman," he said. "Don't tell me she doesn't have a right to be as feminine or masculine as any other woman with her demeanor ... Don't blame it on her hormones."